Microporous catalyst and method for hydrogenating aromatic compounds

ABSTRACT

The invention relates to the hydrogenation of aromatic compounds, in particular the preparation of alicyclic polycarboxylic acids or their esters by core hydrogenation of the corresponding aromatic polycarboxylic acids or their esters, and also to catalysts suitable therefor.

The invention relates to the hydrogenation of aromatic compounds, inparticular the preparation of alicyclic polycarboxylic acids or theiresters by core hydrogenation of the corresponding aromaticpolycarboxylic acids or their esters, and also to catalysts suitabletherefor.

Alicyclic polycarboxylic esters, for example the esters ofcyclohexane-1,2-dicarboxylic acid, are used as lubricant components andas assistants in metal processing. They also find use as plasticizersfor polyolefins and for PVC.

For plasticizing PVC, esters of phthalic acid are used predominantly,for example the dibutyl, dioctyl, dinonyl or didecyl esters. Since theuse of these phthalates has been discussed with increasing controversyin recent times, their use in plastics could be restricted. Alicyclicpolycarboxylic esters, some of which have already been described asplasticizers for plastics in the literature, could then be available assuitable substitutes.

In most cases, the most economical route for preparing alicyclicpolycarboxylic esters is the core hydrogenation of the correspondingaromatic polycarboxylic esters, for example the abovementionedphthalates. Some, processes already exist for this purpose:

U.S. Pat. No. 5,286,898 and U.S. Pat. No. 5,319,129 describe processeswith which dimethyl terephthalate may be hydrogenated over supported Pdcatalysts which are doped with Ni, Pt and/or Ru at temperatures greaterthan or equal to 140° C. and a pressure between 50 and 170 bar to givethe corresponding dimethyl hexahydroterephthalate.

U.S. Pat. No. 3,027,398 discloses the hydrogenation of dimethylterephthalate over supported Ru catalysts at from 110 to 140° C. andfrom 35 to 105 bar.

DE 28 23 165 discloses the hydrogenation of aromatic carboxylic estersover supported Ni, Ru, Rh and/or Pd catalysts to the correspondingalicyclic carboxylic esters at from 70 to 250° C. and from 30 to 200bar. A macroporous support having an average pore size of 70 nm and aBET surface area of approx. 30 m²/g is used.

WO 99/32427 and WO 00/78704 disclose processes for hydrogenatingbenzenepolycarboxylic esters to the corresponding alicyclic compounds.Supported catalysts are used which comprise a metal of transition group,VIII alone or together with at least one metal of transition group I orVII of the Periodic Table and have macropores. A preferred metal oftransition group VIII used is ruthenium. To hydrogenate, three differentcatalyst types are used which differ substantially by their average porediameter and BET surface areas.

Catalyst I: average pore. diameter greater than 50 nm and BET surfacearea less than 30 m²/g

Catalyst II: average pore diameter from 5 to 20 nm and BET surface areagreater than 50 m²/g

Catalyst III: average-pore diameter greater than 100 nm and BET surfacearea less than 15 m²/g

In addition to the pore diameter, the pore volume formed by pores of acertain diameter is specified. The support materials used in thepreparation of catalyst II have a pore distribution in which fromapprox. 5 to approx. 50% of the pore volume by macropores (diameter fromapprox. 50 nm to 10 000 nm) and from approx. 70 to approx. 90% of thepore volume by mesopores (diameter from approx. 2 to 50 nm). The averagepore diameter is between approx. 5 and 20 nm.

The activity and selectivity of hydrogenation catalysts depends on theirsurface properties such as pore size, BET surface area or surfaceconcentration of the active metals.

The catalysts used for the core hydrogenation of aromatic carboxylicacids or their esters should allow a high reaction rate, only generate asmall proportion of by-products and have a long on-stream time.

In a continuously operated process, a catalyst is exposed to mechanical,thermal and chemical stresses which change the pore size and the BETsurface area and thus reduce the activity and selectivity of thiscatalyst.

In addition to mechanical abrasion, many catalysts also exhibit anexpansion of the pore volumes and diameter due to acid digestion.

Aromatic polycarboxylic esters frequently contain small amounts ofcarboxylic acids, and traces of acid additionally form during the corehydrogenation of esters. Partial esters of polycarboxylic acids orpolycarboxylic acids themselves are acidic as a consequence of theirstructure. Therefore, a hydrogenation catalyst suitable for a continuousprocess should be resistant to acid even at relatively high temperaturesunder the hydrogenation conditions.

The surface properties of the catalysts are also responsible for theirreactivity. The existing catalysts are in need of improvement in thisrespect.

It has now been found that, surprisingly, catalysts which comprise atleast one metal of the eighth transition group of the Periodic Table andconsist of a support material having an average pore diameter of from 2to 50 nm and a narrow pore distribution having a fine-pored surfacestructure hydrogenate aromatic carboxylic acids and/or their esters(full or partial esters) in high selectivity and space-time yieldwithout significant side reactions to the corresponding alicyclicpolycarboxylic acids or their esters.

The present invention therefore provides a catalyst for hydrogenatingaromatic compounds to the corresponding alicyclic compounds, saidcatalyst comprising at least one metal of the eighth transition group ofthe Periodic Table on or in a support material, wherein the supportmaterial has an average pore diameter of from 2 to 50 nm and that over91% of the total pore volume of the support materials is accounted forby pores having a diameter of less than 50 nm.

Catalysts of this type may be used particularly for hydrogenatingaromatic compounds. A process for catalytically hydrogenating aromaticcompounds using hydrogen-containing gases over a catalyst whichcomprises at least one metal of the eighth transition group of thePeriodic Table on or in a support material, wherein that the supportmaterial has an average pore diameter of from 2 to 50 nm and over 91% ofthe total pore volume of the support materials is accounted for by poreshaving a diameter of less than 50 nm likewise forms part of the subjectmatter of the present invention.

In principle, the catalysts may comprise any metal of the eighthtransition group of the Periodic Table. The active metals used arepreferably platinum, rhodium, palladium, cobalt, nickel or ruthenium ora mixture of two or more thereof, and ruthenium in particular is used asthe active metal.

In addition to the metals already mentioned, at least one metal of thefirst and/or seventh transition group of the Periodic Table mayadditionally be present in the catalysts. Preference is given to usingrhenium and/or copper.

The content of active metals, i.e. the metals of the first and/orseventh and/or eighth transition group of the Periodic Table isgenerally from 0.1 to 30% by mass. The noble metal content, i.e. themetals of the eighth transition group of the Periodic Table and of thefifth or sixth period, e.g. palladium, ruthenium, calculated as themetal, is in the range from 0.1 to 10% by mass, in particular in therange from 0.8 to 5% by mass, very particularly between 1 and 3% bymass.

To prepare the catalysts according to the invention, support materialshaving an average pore diameter which is in the range from 2 to 50 nmare used. (The average pore diameter is determined by Hg porosimetry, inparticular to DIN 66133.)

In the case of the support materials used, it is possible to distinguishbetween micropores (pore diameter less than 2 nm), mesopores (porediameter from 2 to 50 nm) and macropores (pore diameter greater than 50nm). With regard to the pore type, support materials having thefollowing pore combinations can be used:

a) only mesopores

b) micropores and mesopores

c) mesopores and macropores

d) micropores and mesopores and macropores

e) micropores and macropores

It is decisive for the preparation of the catalysts according to theinvention that, irrespective of the pore size distribution, the averagepore diameter of the support material is between 2 and 50 nm.Preferably, the average pore diameter is from 5 to 24 nm, morepreferably from 10 to 19 nm.

The specific surface area of the support (determined by the BET processby nitrogen adsorption, to DIN 66 131 is 1-350 m²/g, preferably 1-200m²/g, more preferably 1-100 m²/g, in particular 10-90 m²/g or 50-80 m²/gor 1-40 m²/g.

In a specific embodiment of the invention, the catalysts are preparedusing support materials in which over 95%, in particular over 97%, ofthe total pore volume is accounted for by micro- and mesopores, i.e.pores having a diameter of from 2 to 50 nm.

The total pore volume of the catalyst according to the invention is from0.25 to 0.50 ml/g, in particular from 0.28 to 0.43 ml/g.

The carriers used for the preparation of the catalysts according to theinvention are solids whose average pore diameter and whose specificsurface area are within the abovementioned ranges. The carriers used maybe, for example, the following materials: activated carbon, siliconcarbide, aluminum oxide, silicon oxide, aluminosilicate, titaniumdioxide, zirconium dioxide, magnesium oxide and/or zinc oxide or theirmixtures. In addition, these support materials may comprise alkalimetals, alkaline earth metals and/or sulfur.

The starting material used for the preparation of the catalystsaccording to the invention is preferably a titanium hydroxide(metatitanic acid). Metatitanic acid is obtained as an intermediate inTiO₂ preparation according to the classical sulfate process by digestionof ilmenite with sulfuric acid (cf. Ullmann's Encyklopädie dertechnischen Chemie, 4th edition, vol. 18 (1979), p. 574 ff).

The sulfuric acid-containing metatitanic acid, after substantial removalof the sulfuric acid and washing with demineralized water and alsopartial peptizing with nitric acid, is converted to a titanium dioxideof the anatase type by calcining at from 490 to 530° C.

The sulfuric acid may be removed by neutralizing with ammonia or alkalimetal hydroxide solutions and subsequent water washing. Anotherpossibility of deacidification involves washing the sulfuricacid-containing metatitanic acid with water-soluble barium salts, forexample barium nitrate, barium chloride or barium carbonate, and washingwith water. In this case, titanium dioxide is obtained which comprisesbarium salts and possibly small amounts of sulfuric acid and sulfate.

The material obtained in this way is ground to the desired particlesizes and sieved. The calcined TiO₂ powder and/or TiO₂ powder mixturesare homogenized with the addition of water and plasticizing assistant ina mixing apparatus, for example in a kneader or stirrer, and shaped in ashaping apparatus, for example in an extruder or a tableting machine, togive shaped bodies of a desired shape, such as extrudates or tablets.Subsequent drying at 80-120° C. and calcining at 450-550° C. providesthe finished TiO₂ support having the pore structure according to theinvention. For the improvement of the mechanical stability of the TiO2support, it is advantageous, as described in DE 44 19 974, to use a TiO₂powder mixture of at least two powders of different particle sizedistribution for the support preparation.

In the case of the titanium dioxide supports which have been modifiedwith barium salts and are used with preference, the barium content isbetween 1.0 and 4.0% by mass. The content of “free” sulfate may be1.0-5.5% by mass. Free sulfate refers to sulfur, calculated as sulfateof oxidation state 6, which is not present as barium sulfate. Freesulfate may be determined, for example, by titration after oxidativetreatment of the catalyst material in aqueous solution, since bariumsulfate as a very substantially insoluble salt is not included in thedetermination.

The catalysts according to the invention may be obtained by applying atleast one metal of the eighth transition group of the Periodic Table andoptionally at least one metal of the first and/or seventh transitiongroup of the Periodic Table to a suitable support. It is also possibleto prepare the active metals and the support at the same time, i.e. usean unsupported catalyst.

The application may be achieved by saturating the support in aqueousmetal solutions, for example aqueous ruthenium salt solutions, byspraying appropriate metal salt solutions onto the support or by othersuitable processes. Useful metal salts of the first, seventh or eighthtransition group of the Periodic Table include the nitrates, nitrosylnitrates, halides, carbonates, carboxylates, acetylacetonates, chlorocomplexes, nitrito complexes or amine complexes of the appropriatemetals, and preference is given to the nitrates and nitrosyl nitrates.

In the case of catalysts which, in addition to the metal of the eighthtransition group of the Periodic Table, comprise further applied metalsas active metals, the metal salts or metal salt solutions may be appliedat the same time or in succession.

The supports coated or saturated with metal salt solution are thendried, preferably at temperatures of from 80 to 150° C., and optionallycalcined at temperatures of from 200 to 600° C. In the case of separatesaturation, the catalyst is dried after each saturation step andoptionally calcined as described above. The sequence in which the activecomponents are applied can be chosen freely.

Optionally, the application of the active components, drying andcalcining may be effected in one operation, for example by spraying anaqueous metal salt solution onto the support at temperatures over 200°C.

The catalysts according to the invention are advantageously brought intoa shape which offers a low flow resistance on hydrogenation, for exampletablets, cylinders, extrudates or rings. The shaping may be effectedwhen desired at different points in the catalyst preparation.

In the process according to the invention, the hydrogenation is, carriedout in the liquid phase or in the gas phase. The hydrogenation may becarried out continuously or batchwise over suspended catalysts orcatalysts arranged in pieces in a fixed bed. In the process according tothe invention, preference is given to a continuous hydrogenation over acatalyst arranged in a fixed bed in which the product/reactant phase ismainly in the liquid state under the reaction conditions.

When the hydrogenation is carried out continuously over a catalystarranged in a fixed bed, it is advantageous to convert the catalyst intothe active form before the hydrogenation. This may be effected byreducing the catalyst with hydrogen-containing gases by a temperatureprogram. The reduction may optionally be carried out in the presence ofa liquid phase which trickles over the catalyst. The liquid phase usedmay be a solvent or the hydrogenation product.

For the process according to the invention, different process variantsmay be selected. It may be carried out adiabatically, polytropically orvirtually isothermally, i.e. with a temperature rise of typically lessthan 10° C., in one or more stages. In the latter case, all reactors,advantageously tubular reactors, may be operated adiabatically orvirtually isothermally, or else one or more may be operatedadiabatically and the others virtually isothermally. It is also possibleto hydrogenate the aromatic compounds in straight pass or with productrecycling.

Preference is given to carrying out the process according to theinvention in the mixed liquid/gas phase or the liquid phase inthree-phase reactors in cocurrent, and to the hydrogenating gas beingdistributed in the liquid reactant/product stream in a manner known perse. In the interest of uniform liquid distribution, improved removal ofheat of reaction and a high space-time yield, the reactors arepreferably operated with high liquid superficial velocities of from 15to 120, in particular from 25 to 80, m³ per m² of cross section of theempty reactor and hour. When a reactor is operated in straight pass, theliquid hourly space velocity (LHSV) may assume values between 0.1 and 10h⁻¹.

The hydrogenation may be carried out in the absence or preferably in thepresence of a solvent. Useful solvents are any liquids which form ahomogeneous solution with the reactant and product, behave inertly underthe hydrogenation conditions and can be easily removed from the product.The solvent may also be a mixture of several solvents and optionallycomprise water.

For example, the following substances may be used as solvents:

straight-chain or cyclic ethers, for example tetrahydrofuran or dioxane,and also aliphatic alcohols in which the alkyl radical has from 1 to 13carbon atoms.

Alcohols which can be used with preference are isopropanol, n-butanol,isobutanol, n-pentanol, 2-ethylhexanol, nonanols, technical nonanolmixtures, decanol, technical decanol mixtures and tridecanols.

When alcohols are used as solvents, it may be advantageous to use thatalcohol or that alcohol mixture which would be formed on hydrolysis ofthe product. This would rule out by-product formation bytransesterification. A further preferred solvent is the hydrogenationproduct itself.

The use of a solvent allows the aromatic concentration in the reactorfeed to be limited, which allows better temperature control in thereactor. This may have the consequence of minimizing secondary reactionsand thus increasing the product yield. The aromatic content in thereactor feed is preferably between 1 and 35%, in particular between 5and 25%. In the case of reactors which are operated by a loop method,the desired concentration range may be attained via the circulationratio (ratio of recycled hydrogenation effluent to reactant).

The process according to the invention is carried out within a pressurerange of from 3 to 300 bar, in particular between 15 and 200 bar, veryparticularly between 50 and 200 bar. The hydrogenation temperatures arebetween 50 and 250° C., in particular between 100 and 200° C.

The hydrogenating gases used may be any desired hydrogen-containing gasmixtures which do not contain any damaging amounts of catalyst poisons,for example carbon monoxide or hydrogen sulfide. The use of inert gasesis optional, and preference is given to using hydrogen in a purity ofgreater than 95%, in particular greater than 98%. Inert gas constituentsmay be, for example, nitrogen or methane.

The individual reactors may be charged with fresh hydrogen. However, inorder to minimize the hydrogen consumption and the effluent lossesresulting from the offgas, it is advantageous to use the offgas of onereactor as the hydrogenation gas in another reactor. For example, in aprocess which is carried out in two reactors connected in series, it isadvantageous to feed fresh hydrogen into the second reactor and to passthe offgas of the second reactor into the first reactor. In this case,feedstock and hydrogenation gas flow in opposite sequence through thereactors. It is advantageous to maintain the hydrogen excess, based onthe stoichiometric amount required, below 30%, in particular below 10%,very particularly below 5%.

When octyl or nonyl phthalates or their mixtures are converted to thecorresponding 1,2-cyclohexanedicarboxylic esters, preference is given tocarrying out the hydrogenation in the mixed liquid/gas or liquid phasein two reactors connected in series. The first reactor is operated inthe loop method, i.e. a portion of the hydrogenation effluent of thefirst reactor together with fresh reactant is passed into the top of thefirst reactor. The other portion of the effluent of the first reactor ishydrogenated in straight pass in a second reactor. Instead of one largeloop reactor, it is also possible to use a plurality of smaller loopreactors which are arranged in series or in parallel. It is likewisepossible, instead of a large reactor which is flowed through in straightpass, to operate a plurality of reactors which are connected to eachother in series or in parallel. However, preference is given to usingonly one loop reactor and only one reactor which is operated in straightpass. In the process according to the invention, the hydrogenation ofoctyl, nonyl, decyl or dodecyl phthalates is preferably carried outunder the following conditions:

The concentration of these phthalates at the entrance of the firstreactor (loop reactor) is between 1 and 30% by mass, preferably between2 and 10% by mass, most preferably between 3 and 8% by mass. In thehydrogenation effluent of the first reactor, the concentration of thephthalates is between 0.5 and 20% by mass, in particular between 1 and10% by mass.

The liquid hourly space velocity (LHSV, liters of fresh reactant perliter of catalyst per hour) in the loop reactor is from 0.1 to 5 h⁻¹, inparticular from 0.5 to 3 h⁻¹.

The superficial velocity in the loop reactor is in the range from 10 to100 m³/m²/h, preferably in the range from 20 to 80 m³/m²/h, mostpreferably in the range from 40 to 60 m³/m²/h.

The average hydrogenation temperatures in the loop reactor are from 60to 150° C., in particular from 70 to 120° C.

The hydrogenation pressure in the loop reactor is from 25 to 200 bar, inparticular from 80 to 110 bar.

In the effluent of the second reactor, the concentration of reactant isless than 0.3% by mass, in particular less than 0.1% by mass, veryparticularly less than 0.05% by mass.

The liquid hourly space velocity in the second reactor (liters of nonylphthalate per liter of catalyst per hour) is from 1 to 20 h⁻¹, inparticular from 2 to 10 h⁻¹.

In the second reactor, the average temperature is between 60 and 150°C., in particular 70 and 120° C.

The hydrogenation pressure in the second reactor is from 25 to 200 bar,in particular from 80 to 110 bar.

The process according to the invention allows aromatic compounds such asaromatic poly- and/or monocarboxylic acids or their derivatives, inparticular their alkyl esters, to be converted to the correspondingalicyclic polycarboxylic acid compounds. Both full esters and partialesters may be hydrogenated. A full ester is a compound in which all acidgroups are esterified. Partial esters are compounds having at least onefree acid group (or optionally an anhydride group) and at least oneester group.

When polycarboxylic esters are used in the process according to theinvention, these preferably contain 2, 3 or 4 ester functions.

The aromatic compounds or polycarboxylic esters used in the processaccording to the invention are preferably polycarboxylic acids ofbenzene, diphenyl, naphthalene and/or anthracene, their anhydridesand/or the corresponding esters. The resulting alicyclic polycarboxylicacids or their derivatives consist of one or more C₆ rings, optionallylinked via a C—C bond or fused on.

The alcohol component of the carboxylic esters used preferably consistsof branched or unbranched alkyl, cycloalkyl, or alkoxyalkyl groupshaving from 1 to 25 carbon atoms. These may be identical or differentwithin one molecule of a polycarboxylic ester, i.e. they may beidentical or different isomers or possess an identical or differentnumber of carbon atoms. It will be appreciated that it is also possibleto use isomers with regard to the substitution pattern of the aromaticsystem in the form of a mixture, for example a mixture of phthalic esterand terephthalic ester.

In a preferred embodiment, the present invention relates to a processfor hydrogenating benzene-1,2-, -1,3-, or -1,4-dicarboxylic esters,and/or benzene-1,2,3-, -1,2,4-, or -1,3,5-tricarboxylic esters, i.e. theisomers of cyclohexane-1,2-, -1,3-, or -1,4-dicarboxylic esters, or ofcyclohexane-1,2,3-, -1,3,5-, or -1,2,4-tricarboxylic esters areobtained.

Esters of the following aromatic carboxylic acids, for example, may beused in the process of the invention: naphthalene-1,2-dicarboxylic acid,naphthalene-1,3-dicarboxylic acid, naphthalene-1,4-dicarboxylic acid,naphthalene-1,5-dicarboxylic acid, naphthalene-1,6-dicarboxylic acid,naphthalene-1,7-dicarboxylic acid, naphthalene-1,8-dicarboxylic acid,phthalic acid (benzene-1,2-dicarboxylic acid), isophthalic acid(benzene-1,3-dicarboxylic acid), terephthalic acid.(benzene-1,4-dicarboxylic acid), benzene-1,2,3-tricarboxylic acid,benzene-1,2,4-tricarboxylic acid (trimellitic acid),benzene-1,3,5-tricarboxylic acid (trimesic acid) orbenzene-1,2,3,4-tetracarboxylic acid. It is also possible to use acidswhich are produced from the acids mentioned by substituting one or moreof the hydrogen atoms bonded to the aromatic core with alkyl,cycloalkyl, or alkoxyalkyl groups.

It is possible to use alkyl, cycloalkyl, or else alkoxyalkyl esters, forexample, of the abovementioned acids, these radicals each independentlyincluding from 1 to 25, in particular from 3 to 15, very particularlyfrom 8 to 13, particularly 9, carbon atoms. These radicals may be linearor branched. If a starting material has more than one ester group, theseradicals may be identical or different.

Examples of compounds which may be used in the process of the inventionas esters of an aromatic polycarboxylic acid are the following:monomethyl terephthalate, dimethyl terephthalate, diethyl terephthalate,di-n-propyl terephthalate, dibutyl terephthalate, diisobutylterephthalate, di-tert-butyl terephthalate, monoglycol terephthalate,diglycol terephthalate, n-octyl terephthalate, diisooctyl terephthalate,di-2-ethylhexyl terephthalate, di-n-nonyl terephthalate, diisononylterephthalate, di-n-decyl terephthalate, di-n-undecyl terephthalate,diisodecyl terephthalate, diisododecyl terephthalate, ditridecylterephthalate, di-n-octadecyl terephthalate, diisooctadecylterephthalate, di-n-eicosyl terephthalate, monocyclohexyl terephthalate;monomethyl phthalate, dimethyl phthalate, di-n-propyl phthalate,di-n-butyl phthalate, diisobutyl phthalate, di-tert-butyl phthalate,monoglycol phthalate, diglycol phthalate, di-n-octyl phthalate,diisooctyl phthalate, di-2-ethylhexyl phthalate, di-n-nonyl phthalate,diisononyl phthalate, di-n-decyl phthalate, di-2-propylheptyl phthalate,diisodecyl phthalate, di-n-undecyl phthalate, diisoundecyl phthalate,ditridecyl phthalate, di-n-octadecyl phthalate, diisooctadecylphthalate, di-n-eicosyl phthalate, monocyclohexyl phthalate,dicyclohexyl phthalate, monomethyl isophthalate, dimethyl isophthalate,dimethyl isophthalate, diethyl isophthalate, di-n-propyl isophthalate,di-n-butyl isophthalate, diisobutyl isophthalate, di-tert-butylisophthalate, monoglycol isophthalate, diglycol isophthalate, di-n-octylisophthalate, diisooctyl isophthalate, 2-ethylhexyl isophthalate,di-n-nonyl isophthalate, diisononyl, isophthalate, di-n-decylisophthalate, diisodecyl isophthalate, di-n-undecyl isophthalate,diisododecyl isophthalate, di-n-dodecyl isophthalate, ditridecylisophthalate, di-n-octadecyl isophthalate, diisooctadecyl isophthalate,di-n-eicosyl isophthalate, monocyclohexyl isophthalate.

The process according to the invention can in principle also be appliedto benzoic acid and its esters. These include benzoates of diols, forexample glycol dibenzoate, diethylene glycol benzoate, triethyleneglycol dibenzoate and propylene glycol dibenzoate, and also alkylbenzoates. The alcohol component of the alkyl benzoates may consist offrom 1 to 25, preferably from 8 to 13, carbon atom(s). The alcohols maybe linear or branched.

It is also possible to use mixtures of two or more polycarboxylicesters. Examples of such mixtures may be obtained in the following ways:

-   -   a) A polycarboxylic acid is partially esterified using an        alcohol in such a way as to give both full and partial esters.    -   b) A mixture of at least two polycarboxylic acids is esterified        using an alcohol, producing a mixture of at least two full        esters.    -   c) A polycarboxylic acid is treated with an alcohol mixture, and        the product may be a mixture of full esters.    -   d) A polycarboxylic acid is partially esterified using an        alcohol mixture.    -   e) A mixture of at least two carboxylic acids is partially        esterified using an alcohol mixture.    -   f) A mixture of at least two polycarboxylic acids is partially        esterified using an alcohol mixture.

Instead of the polycarboxylic acids in reactions a) to f), theiranhydrides may also be used.

Aromatic esters are frequently prepared industrially from alcoholmixtures, in particular the full esters by route c).

Examples of corresponding alcohol mixtures include:

C₅ alcohol mixtures prepared from linear butenes by hydroformylationfollowed by hydrogenation;

C₅ alcohol mixtures prepared from butene mixtures which comprise linearbutene and isobutene, by hydroformylation followed by hydrogenation;

C₆ alcohol mixtures prepared from a pentene or from a mixture of two ormore pentenes, by hydroformylation followed by hydrogenation;

C₇ alcohol mixtures prepared from triethylene or dipropene or from ahexene isomer or from another mixture of hexene isomers, byhydroformylation followed by hydrogenation;

C₈ alcohol mixtures, such as 2-ethylhexanol (2 isomers), prepared byaldol condensation of n-butyraldehyde followed by hydrogenation;

C₉ alcohol mixtures prepared from C₄ olefins by dimerization,hydroformylation, and hydrogenation. The starting materials forpreparing the C₉ alcohols may be isobutene or a mixture of linearbutenes or mixtures of linear butenes and isobutene. The C₄ olefins maybe dimerized with the aid of various catalysts, for example proticacids, zeolites, organometallic nickel compounds, or solid nickelcatalysts. The C₈ olefin mixtures may be hydroformylated with the aid ofrhodium catalysts or cobalt catalysts. There is therefore a wide varietyof industrial C₉ alcohol mixtures.

C₁₀ alcohol mixtures prepared from tripropylene by hydroformylationfollowed by hydrogenation; 2-propylheptanol (2 isomers) prepared byaldol condensation of valeraldehyde followed by hydrogenation;

C₁₀ alcohol mixtures prepared from a mixture of at least two C₅aldehydes by aldol condensation followed by hydrogenation;

C₁₃ alcohol mixtures prepared from hexaethylene, tetrapropylene, ortributene, by hydroformylation followed by hydrogenation.

Other alcohol mixtures may be obtained by hydroformylation followed byhydrogenation from olefins or olefin mixtures which arise, for example,in Fischer-Tropsch syntheses, in dehydrogenations of hydrocarbons, inmetathesis reactions, in the polygas process, or in other industrialprocesses.

Olefin mixtures with olefins of differing carbon numbers may also beused to prepare alcohol mixtures.

In the process of the invention, any ester mixture prepared fromaromatic polycarboxylic acids and the abovementioned alcohol mixturesmay be used. According to the invention, preference is given to estersprepared from phthalic acid or phthalic anhydride and a mixture ofisomeric alcohols having from 6 to 13 carbon atoms.

Examples of industrial phthalates which can be used in the process ofthe invention include products with the following trade names:

Vestinol C (di-n-butyl phthalate) (CAS No. 84-74-2); Vestinol IB(diisobutyl phthalate) (CAS No. 84-69-5); Jayflex DINP (CAS No.68515-48-0); Jayflex DIDP (CAS No. 68515-49-1); Palatinol 9P(68515-45-7), Vestinol 9 (CAS No. 28553-12-0); TOTM (CAS No. 3319-31-1);Linplast 68-TM, Palatinol N (CAS No. 28553-12-0); Jayflex DHP (CAS No.68515-50-4); Jayflex DIOP (CAS No. 27554-26-3); Jayflex. UDP (CAS. No.68515-47-9); Jayflex DIUP (CAS No. 85507-79-5); Jayflex DTDP (CAS No.68515-47-9); Jayflex L9P (CAS NO. 68515-45-7); Jayflex L911P (CAS No.68515-43-5); Jayflex L11P (CAS No. 3648-20-2); Witamol 110 (CAS No.68515-51-5); Witamol 118 (di-n-C8-C10-alkyl phthalate) (CAS No.71662-46-9); Unimoll BB (CAS No. 85-68-7); Linplast 1012 BP (CAS No.90193-92-3); Linplast 13XP (CAS No. 27253-26-5); Linplast 610P (CAS No.68515-51-5); Linplast 68 FP (CAS No. 68648-93-1); Linplast 812 HP (CASNo. 70693-30-0); Palatinol AH (CAS No. 117-81-7); Palatinol 711 (CAS No.68515-42-4); Palatinol 911 (CAS No. 68515-43-5); Palatinol 11 (CAS No.3648-20-2); Palatinol Z (CAS No. 26761-40-0); Palatinol DIPP (CAS No.84777-06-0); Jayflex 77 (CAS No. 71888-89-6); Palatinol 10 P (CAS No.53306-54-0); Vestinol AH (CAS No. 117-81-7).

It is pointed out that the core hydrogenation of each isomer used in thecore hydrogenation of aromatic polycarboxylic acids or their esters mayresult in at least two stereoisomeric hydrogenation products. The ratiosof the resulting stereoisomers to each other depend on the catalyst usedand on the hydrogenation conditions.

All hydrogenation products having any desired ratio(s) of thestereoisomers to each other may be used without separation.

The invention further provides the use of the alicyclic polycarboxylicesters prepared according to the invention as plasticizers in plastics.Preferred plastics include PVC, homo- and copolymers based on ethylene,propylene, butadiene, vinyl acetate, glycidyl acrylate, glycidylmethacrylate, acrylates, acrylates having alkyl radicals of branched orunbranched alcohols having from one to ten carbon atom(s) bonded to theoxygen atom of the ester group, styrene or acrylonitrile, or homo- orcopolymers of cyclic olefins.

Examples of representatives of the above groups include the followingplastics:

polyacrylates having the same or different alkyl radicals having from 4to 8 carbon atoms bonded to the oxygen atom of the ester group, inparticular having the n-butyl, n-hexyl, n-octyl, 2-ethylhexyl orisononyl radical, polymethacrylate, polymethyl methacrylate, methylacrylate-butyl acrylate copolymers, methyl methacrylate-butylmethacrylate copolymers, ethylene-vinyl acetate copolymers, chlorinatedpolyethylene, nitrile rubber, acrylonitrile-butadiene-styrenecopolymers, ethylene-propylene copolymers, ethylene-propylene-dienecopolymers, styrene-acrylonitrile copolymers, acrylonitrile-butadienerubber, styrene-butadiene elastomers, methylmethacrylate-styrene-butadiene copolymers and/or nitrocellulose.

Furthermore, the alicyclic polycarboxylic esters prepared according tothe invention may be used for modifying plastic mixtures, for examplethe mixture of a polyolefin with a polyamide.

Mixtures of plastics and the alicyclic polycarboxylic esters preparedaccording to the invention likewise form part of the subject matter ofthe present invention. Suitable plastics are the compounds alreadymentioned. Such mixtures preferably comprise at least 5% by weight, morepreferably 20-80% by weight, most preferably 30-70% by weight, of thealicyclic polycarboxylic esters.

Mixtures of plastics, in particular PVC, which comprise one or more ofthe alicyclic polycarboxylic esters prepared according to the inventionmay, for example, be present in the following products or be used fortheir preparation: casings for electrical equipment, for example kitchenappliances, computer casings, casings and components of phonographic andtelevision equipment, pipes, apparatus, cables, wire sheaths insulatingtapes or window profiles, in interior decoration, in vehicle andfurniture construction, plastisols, floor coverings, medical products,food packaging, seals, films, composite films, phonographic disks,synthetic leather, toys, packaging containers, adhesive tape films,clothing, coatings and as fibers for fabrics.

In addition to the abovementioned applications the alicyclicpolycarboxylic esters prepared according to the invention may also beused as a lubricant component, or as a constituent of cooling liquidsand metalworking fluids. They may likewise be used as a component indyes, paints, inks and adhesives.

The examples which follow are intended to illustrate the invention,without restricting its field of application which can be discerned fromthe description and the patent claims.

EXAMPLE 1

Preparation of a Titanium Dioxide Support for a Catalyst According tothe Invention

Commercially obtainable metatitanic acid (H₂TiO₃), an aqueous suspensionwhich formally contains 30% by mass of titanium dioxide and 11% by massof sulfuric acid was filtered with the aid of a filter press. For every1 kg of suspension used, the filter cake was washed with 5000 g ofwater. The damp filter cake formally had a content of 41.5% by mass oftitanium dioxide and 5.3% by mass of sulfuric acid.

85 g of barium nitrate were added at room temperature to a suspension of3000 g of filter cake and 3500 g of water in a 10 l stirred tank. Theaddition of barium nitrate resulted in a portion of the sulfuric acidbeing converted to barium sulfate. After stirring for one hour at roomtemperature, the suspension was filtered. The filter cake obtained wasdried at 110° C. for five hours and then calcined at 520° C. for 3hours. In this time, the content of “free sulfate” in the form of sulfurtrioxide was further reduced.

The solid obtained formally contained 91.5% by mass of titanium dioxide,5.5% by mass of barium sulfate and 3.1% by mass of free sulfate. Thissolid was ground to give two powder types and the desired particle sizefraction was sieved out. One powder consisted of particles havingparticle sizes of from 1 to 30 μm, and the other powder of particleshaving particle sizes of from 20 to 500 μm. The two different powdertypes were mixed in a 1/1 ratio. To each 1 kg of powder mixture, 13 g ofpolyethylene oxide (Polyox WSR 301, manufacturer Union CarbideCorporation), 13 g of methylcellulose (Culminal MPHC 50, manufacturerAqualon-Hercules GmbH), 70 g of glass fibers (8031, manufacturer BayerAG), 70 g of ethylene glycol and 200 g of water were added. Theresulting mixture was homogenized in a kneader and then shaped with theaid of an extruder into extrudates in the form of a cylinder having acircular diameter of 1.5 mm and a length of from 4 to 6 mm. Theextrudates were dried at 80° C. for three hours and then calcined at450° C. for five hours.

The physical parameters of the support A for the catalyst according tothe invention prepared according to example 1 were compiled in table 1.As a comparison, the parameters of a support B frequently used inindustry, from which no catalyst according to the invention can beprepared, are listed. TABLE 1 Properties of the carriers used Averagepore Proportion of BET surface diameter in nm Proportion of the porevolume area in g/m² to DIN 66133 Total pore the pore of the sum ofManufacturer to DIN 66131 (Hg volume in volume of the mesopores and ortype Material (N₂ adsorption) porosimetry) ml/g macropores in %micropores in % designation A: TiO₂ 75 14.8 0.33 <2 >98 H 9063 B:α-Al₂O₃ 7 206.5 0.64 >97 <3 Axence SP 512 non-inventive

The total pore volume was determined from the sum of the pore volumes ofthe pores having a pore diameter >7.6 nm (determined by Hg porosimetry)and pores having a pore diameter <7.6 nm (determined by the N₂adsorption method).

EXAMPLES 2 AND 3

Preparation of the hydrogenation catalysts A and B For the preparationof hydrogenation catalysts based on the supports detailed in table 1,the supports were first dried at 80° C. After drying, the supports weresaturated or spray-dried with an aqueous ruthenium(III) nitrate solutionwhich contained a ruthenium concentration of 0.8% by weight.

For the saturation of the support, the Ru solution in nitric acid wasdiluted with water to a volume corresponding to the pore volume of thesupport.

The Ru solution was applied to the support material by dropwiseapplication or preferably by uniform spraying while circulating thesupport. After drying at 120° C. under nitrogen, the support coated withruthenium salt was activated (reduced) in a hydrogen/nitrogen mixture,(ratio 1:9) at 200° C. for over 6 hours.

N.B.: The catalysts prepared in this way were referred to in thefollowing text by the same capital letters as the parent supports, andthe active metal and its contents were reported in subsequent brackets.

EXAMPLES 3-6

The hydrogenation experiments were carried out according to thefollowing general method:

90.7 g of the catalyst were initially charged in a catalyst basket,cautiously reduced in a 1000 ml pressure reactor in a hydrogen streamaccording to the above method and then admixed with 590 g of liquiddiisononyl phthalate (Vestinol 9, OXENO Olefinchemie GmbH). The DINP washydrogenated with pure hydrogen. After hydrogenating the startingmaterial, the reactor was decompressed and the reaction mixture wasanalyzed by means of gas chromatography for its content of the targetproduct diisononyl cyclohexane-1,2-dicarboxylate (DINCH). The conversionof DINP was always above 99.9%.

The experimental conditions of the hydrogenation examples and theirresults were compiled in table 2: TABLE 2 DINPhydrogenation/hydrogenation examples Hyrdogenation Pressure TemperatureReaction time Content of examples Catalyst Reactant in bar in ° C. inhours DINCH in % 3 A (1% Ru) DINP 200 80 2.5 99.4 4 A (1% Ru) DINP 200100 1 99.3 5 A (1% Ru) DINP 50 120 0.8 99.6 6 B (1% Ru) DINP 200 80 2099.4 Comparative example

It can thus be demonstrated that the type A catalyst according to theinvention exhibits a distinctly higher hydrogenation activity thancatalyst B.

1. A catalyst comprising at least one metal of the eighth transitiongroup of the Periodic Table on or in a support material, wherein thesupport material comprises titanium dioxide which may further comprisean alkali metal, an alkaline earth metal and/or sulfur, and has anaverage pore diameter of from 2 to 50 nm and over 95% of the total porevolume of the support material is accounted for by pores having adiameter of less than 50 nm.
 2. The catalyst as claimed in claim 1,wherein the specific surface area of the support material is between 1and 350 m²/g.
 3. The catalyst as claimed in claim 1, wherein the supportmaterial consists of titanium dioxide having a content of from 1.0 to5.5% by mass of free sulfate.
 4. The catalyst as claimed in claim 1,wherein the support material consists of titanium dioxide having acontent of from 1.0 to 4.0% by mass of barium.
 5. The catalyst asclaimed in claim 1, wherein the catalyst additionally comprises at leastone metal of the first transition group of the Periodic Table.
 6. Thecatalyst as claimed in claim 1, wherein the catalyst further comprisesat least one metal of the seventh transition group of the PeriodicTable.
 7. A process for catalytically hydrogenating an aromaticpolycarboxylic and/or monocarboxylic acid compound or a derivativethereof to the corresponding alicyclic compound comprising hydrogenatingsaid aromatic polycarboxylic and/or monocarboxylic acid compound with ahydrogen-containing gas over a catalyst which comprises at least onemetal of the eighth transition group of the Periodic Table on or in asupport material, wherein the support material comprises titaniumdioxide which may further comprise an alkali metal, an alkaline earthmetal and/or sulfur, and has an average pore diameter of from 2 to 50 nmand over 95% of the total pore volume of the support materials isaccounted for by pores having a diameter of less than 50 nm.
 8. Theprocess as claimed in claim 7, wherein the specific surface area of thesupport material is between 1 and 350 m²/g.
 9. The process as claimed inclaim 7, wherein the support material consists of titanium dioxidehaving a content of from 1.0 to 5.5% by mass of free sulfate.
 10. Theprocess as claimed in claim 7, wherein the support material consists oftitanium dioxide having a content of from 1.0 to 4.0% by mass of barium.11. The process as claimed in claim 7, wherein the catalyst furthercomprises at least one metal of the first transition group of thePeriodic Table.
 12. The process as claimed in claim 7, wherein thecatalyst further comprises at least one metal of the seventh transitiongroup of the Periodic Table.
 13. The process as claimed in claim 7,wherein said aromatic polycarboxylic and/or monocarboxylic acid compoundor said derivative thereof is a carboxylic acid of benzene, diphenyl,naphthalene, diphenyl oxide or anthracene, its anhydride and/or acorresponding ester.
 14. The process as claimed in claim 13, wherein thealcohol component of the carboxylic ester is alkoxyalkyl, cycloalkyland/or an alkyl group having from 1 to 25 carbon atoms, branched orunbranched, each the same or different.
 15. A hydrogenation processcomprising hydrogenating a compound with the catalyst as claimed inclaim
 1. 16. A hydrogenation process as claimed in claim 15 wherein saidcompound is an aromatic polycarboxylic and/or monocarboxylic acid or aderivative thereof.
 17. A hydrogenation process as claimed in claim 16wherein said aromatic polycarboxylic and/or monocarboxylic acid orderivative thereof is hydrogenated to the corresponding alicyliccompounds.